This invention relates to an electric water heater, particularly to an electric water heater having an electronic control and detection system that greatly reduces expense and improves operating efficiencies.
Typical electric water heaters are constructed with one or two electric-powered heating elements to heat water in the water tank, depending on the size and utilization of the water heater. Each element is ordinarily mounted onto a side wall of the tank. Further, in designs incorporating two elements, the elements are typically mounted onto the tank at spaced separation from one another. There are a number of disadvantages associated with such constructions. Element malfunction is not easily detected and is also costly since monitoring devices are required in the overall design. Also, the monitoring devices themselves can malfunction and not detect element failure. In addition, it is often difficult to identify the source of a malfunction, which works to increase the time required for repair and/or replacement of a defective or malfunctioning part.
Another significant problem with present construction is the difficulty of protecting against xe2x80x9cdry firedxe2x80x9d elements. xe2x80x9cDry firexe2x80x9d occurs when power is applied to a heating element without water surrounding the element. Such dry firing rapidly causes damage to the heating element, thereby sharply reducing its useful life span. In most instances, dry firing can cause immediate failure of the element.
Dry fire often occurs because electric water heaters typically use heating elements that have watt densities that are usually too high to allow operation in air without damage. These less expensive elements will bum out if energized in air for as little as 30 seconds. This fact causes a problem during installation or service of electric heaters because if the installer forgets and switches on the power before the tank is full of water, the upper element will be destroyed. These mistakes are common enough that dry fire service costs are significant and thus effort has been made to develop a heater control system that will prevent the problem.
One approach to the dry fire problem is to energize the element and watch the temperature change with the temperature sensor located just above the element. Such a system is disclosed, for example, in U.S. Pat. No. 5,442,157 to Jackson. This system works if the temperature sensor is responsive enough that a temperature change can be detected before the element reaches a temperature that causes damage. In the case of a water heater tank, however, the thickness of the steel tank wall and the rate of heating of the element are such that the sensor is normally not responsive enough.
The conventional approach is to only turn the element on for a short period and then watch for a temperature change. This works for a specific range of element watt densities but does not work when a range of different wattage elements are used. To detect a dry tank over a broad range of element types the element has to be pulsed repeatedly over a period of time. The pulsing prevents the high watt density elements from getting too hot and allows the low temperature heat input of the low watt density elements to have time to be detected.
This invention has been developed in view of the foregoing to overcome the deficiencies of the prior art.
It is an object of the invention to provide a water heater that increases energy efficiency.
It is another object of the invention to provide a water heater that protects against dry firing of heating elements.
Other objects and advantages of the invention will become apparent to those skilled in the art from the drawings, the detailed description of the invention, and the appended claims.
The water heater of the present invention includes a water container; an element located to heat water in the water container; a sensor located to sense temperature proximate the element; and a controller connected to the element and the sensor. The controller is programmed to energize the element with at least one electrical pulse over a predetermined time interval, comparing temperature information received from the sensor with a predetermined temperature, and disengaging the element in the event that the temperature received from the sensor is greater than a predetermined temperature for the predetermined time interval.